DSolve[-Sqrt[(b0 + b1*y[x] + b2*y[x]^2 + b3*y[x]^3 + b4*y[x]^4)/(a0 + a1*x + a2*x^2 + a3*x^3 + a4*x^4)] + Derivative[1][y][x] == 0,y[x],x]